The present invention relates to a rolling element for use in a continuously variable transmission (CVT), such as a toroidal CVT, for automobiles. More specifically, this invention relates to the rolling element for the CVT which is improved in rolling contact fatigue life, and a method for producing the rolling element.
The toroidal CVT includes an input disk, an output disk and power rollers interposed between the input and output disks. Each of the power rollers includes inner and outer races and a plurality of balls between the races. The races have bearing surfaces contacted with the balls via lubricating oil. The inner race of the power roller has a traction surface contacted with a traction surface of each of the disks via lubricating oil. Rotation of the input disk is transmitted to the output disk by the traction drive produced between the traction surfaces of the disks and the traction surfaces of the power rollers.
U.S. Pat. No. 5,556,348 discloses input and output disks and a power roller for a toroidal CVT, which have traction surfaces formed by carburizing and finish grinding. U.S. Pat. No. 6,051,080 discloses a power roller for a toroidal CVT. A race of the power roller has a bearing surface formed by carburizing and finish grinding.
Further, Japanese Patent Application First Publication No. 5-301165 discloses a method for improving bending-fatigue strength of a carburized and quenched member. The carburized and quenched part having a surface abnormal-structure layer is subjected to shot peening to transform the surface abnormal-structure layer to martensite. Shots used in the shot peening have a particle diameter of not more than 0.1 mm.